Current and proposed work for the next budget year will be concentrated in the following areas: 1) Further study of the microvasculature of the teleost ventricle, 2) Quantification of blood supply to the ventricle, both from coronary arteries and luminal flow, 3) Comparison of conary supplies in various phyla to explore evoluntionary development of coronary arterial supply, and 4) Study of changes in blood flow distribution brought about by hypoxia, exercise, and pharmacological agents. A combination of methods will be applied to these problems, including indicator dilution techniques using isotopes and isotope-labeled microspheres, histological location of injected microsphere loads, vascular casting combined with scanning electron microscopy, and quantitative measurement of blood flow by electromagnetic and thermal means. The overall objective of the studies is to further understanding of blood flow distribution and its control in teleosts, and to compare the findings with similar systems in the higher vertebrates. By proceeding from simpler to more complex circulatory systems, we hope to gain better understanding of the system design considerations common to all.